Hydrogen cyanide as an alternative fumigant for stored product pests in the USA

We investigated hydrogen cyanide (HCN), a well-known and highly effective fumigant as an alternative to phosphine (PH3) and methyl bromide. Laboratory experiments were conducted with PH3-resistant and susceptible populations of the red flour beetle (RFB), Tribolium castaneum and the lesser grain borer (LGB), Rhyzopertha dominica, and found no differences in their susceptibility to HCN based on PH3 resistance. Toxicity experiments on these two species showed that RFBs were more tolerant of HCN compared to LGB being more susceptible. Comparisons of life stage mortality to HCN found that eggs were easy to kill in both species, while adults, larvae and pupae required higher concentrations. Mixed life-stage colonies were treated with different concentrations of HCN for 24 h so that all immature stages and adults of different ages were exposed at the same time. Treatments to mixed life-stage colonies ranging from 636 to 1500 ppm of HCN killed colonies of both species, with no adult emerge after treatment.  Thus, all adults and immature life stages were killed with these concentrations. Similar experiments with HCN were conducted on the beetle species Trogoderma variabile, Cryptolestes ferrugineus¸ Oryzaephilus surinamensis, Lasioderma serricorne, and the moth Plodia interpunctella. L. serricorne was by far the most HCN-tolerant species among them, requiring over 2,500 ppm HCN to prevent any live adults to emerge from mixed-life stage cultures. Other experiments reveled that HCN headspace concentrations went down markedly in the presence of grain and other foods. Effective applications will require careful attention to sorption, and the amount of gas used.